Electromagnetic alternating current switching device



Feb. 15, 1966 R. J. WEBB ELECTROMAGNETIC ALTERNATING CURRENT SWITCHING DEVICE Filed Dec. 6, 1961 fff 1 W; 6

Roger J. Webb HIS INVENTOR.

TTORNEY United States Patent 3,235,744 ELECTROMAGNETIC ALTERNATING CURRENT SWITCHING DEVICE Roger J. Webb, London, England, assignor to Westinghouse Brake and Signal Company, Limited, London, England Filed Dec. 6, 1961, Ser. No. 157,345 Claims priority, application Great Britain, Dec. 9, 1960, 42,425/60 4 Claims. (Cl. 30788) My invention relates to an electromagnetic alternating current switching device. More particularly my invention relates to such a switching device which may be selectively controlled to on and off states in accordance with the polarity of direct current control signals supphed thereto and which also, if each such control signal comprises a pulse of direct current, has provisions for retaining a memory of the state to which the devlce was last controlled. I

In an alternating current switching system it 1s sometimes necessary to provide means to insure that, should the alternating current supply be cut off to the system or to some component of the system, there is no loss of instructions stored in the system or that component of it. In order to achieve this it is necessary to employ a SWltChing device whose state, after the alternating current has been restored, is a function of the last control signal fed to it, regardless of when this control signal is received 111 relation to the period of supply failure.

It is an object of the present invention to provide an improved switching device which will fulfil the above function.

In accomplishing the above object of my invention I employ a switching device including a magnetic core which is provided with an alternating current winding arrangement, the core being incorporated into the magnetic circuits of a permanent magnet, and the magnetic circuits of an electromagnet which is arranged to be energized by a direct current control signal, and the device being so arranged that the inductance of the alternating current winding arrangement may be switched between two values by reversing the polarity of the control signal. A memory of the switching is maintained when the control signal is removed by means of remanent magnetism present in the magnetic circuit of the switching device.

Other objects and characteristic features of my invention will become apparent as the description proceeds.

In the accompanying drawings:

FIG. 1 represents diagrammatically a switching device having a core arranged according to the present invention, and

FIG. 2 shows the magnetization curve of the core of the device of FIG. 1.

In carrying the invention into efiect, according to one convenient mode by way of example, a switching device as shown in FIG. 1 includes a rectangular four-limbed core C constructed from laminations of a high permeability material, such as a nickel-iron alloy, carrying windings W1 and W2 wound upon two opposed limbs L1 and L2, respectively. A load LD is connected in series with windings W1 and W2 which are also connected in series with each other so as to produce series aiding fluxes in core C when a source of alternating current has its terminals connected across terminals 6 and 7 as shown in FIG. 1.

3,235,744 Patented Feb. 15, 1966 The core C is interposed between two magnetic systems, one being a permanent magnet M having pole pieces P1 and P2, and the other being an electromagnet EM consisting of a winding W3 connected across terminals designated 8 and 9 and wound upon a core C1 having pole pieces P3 and P4. Air gaps G1 and G2 are included in the permanent magnet circuit to provide adjustment for initial setting up of the circuit.

The cross-sectional area of core C is so proportioned, in accordance with the alternating current supply frequency and voltage, that windings W1 and W2 can each be limited to a number of turns which can be accommodated upon limbs L1 and L2 with adequate mechanical isolation and electrical insulation from each other, thereby ensuring the prevention of short circuits between them.

The magnetizing characteristics of core C are as shown in FIG. 2, with the core saturating at a flux level as a result of a predetermined value of magnetomotive force M.M.F. The alternating current supply voltage is so selected that the alternating current flux swing in core C is small compared with the saturation flux level 5 A reasonable proportion is considered to be one third.

The core material for the core C1 of electromagnet EM is chosen so that it will exhibit remanent magnetism. In this way the core C1 will remain magnetized in a particular north-sou'ih configuration depending upon the polarity of the last DC. control current supplied across terminals 3 and 9 of winding W3, even after this control current has ceased to exist or when it comprises merely a pulse of direct current. The power to winding W3 is supplied from a suitable source of reversible polarity direct current as shown in FIG. 1. The direct current can be either continuous or pulsed and of either polarity according to the control desired.

With the arrangement shown in FIG. 1, flux due to permanent magnet M is distributed in core C in the following way. With the north-south configuration shown, flux will flow from A1 directly to B1 and also from A1 to B1 via a second path A1, A2, B2, B1. By suitable choice of the geometry of core C, the flux densities in the two paths A1, B1; and A1, A2, B2, B1 are in the ratio 3 t 1.

Similarly any flux from the electromagnet EM will be divided in the ratio 3:1 along the paths A2, B2 (or B2, A2), and A2, A1, B1, B2 (or B2, B1, A1, A2), respectively, depending on the polarity of the control current last supplied to winding W3. If a pulse of direct current is supplied across terminals 8 and 9 and flows in winding W3, thereby magnetizing core C1 of electromagnet EM so that the pole pieces P3 and P4 are made south and north poles respectively, then the total fluxes in the limbs of the core C due to the magnetic systems of magnet M and electromagnet EM will be as follows.

Fluxes oppose one another in limbs L1 and L2 and aid one another in limbs L3 and L4. The total flux density in limbs L3 and L4 is such that the alternating current flux charge due to windings W1 and W2 cannot be fully realized in core C. By suitable proportioning of the magnetic circuit, the total flux density in limbs L3 and L4 can be made at least equal to the saturation flux density d, of the material. In this case windings W1 and W2 will then possess zero inductance.

If new the direct current supplied across terminals 8 and 9 and flowing in winding W3 is reversed in polarity so that P3 becomes a north pole and P4 a south pole, fluxes will aid one another in limbs L1 and L2 and oppose one another in limbs L3 and L4. Due to the geometry of core C, the total flux density in each limb will be 3 approximately the same. By suitable adjustment of air gaps G1 and G2, the total alternating current flux charge due to windings W1 and W2 can be realized in core C, and windings W1 and W2 will possess a significant inductance.

In this way, two distinct output conditions or states are provided depending upon the polarity of control current supplied to winding W3.

In terms of load current, these conditions are:

(i) A low current associated with core C and windings W1 and W2 When alternating current flux charge can be realized and windings W1 and W2 possess inductance.

(ii) A higher current limited only by the resistance of windings W1 and W2 and the impedance of load Ll) when the core C is saturated and windings W1 and W2 possess zero inductance.

By the use of a suitable core material for core C1 of electromagnet EM which exhibits permanent magnet properties, that is, remanent magnetism, and whose state of magnetization is a function of the polarity of the last direct current supplied to winding W3, a device is provided which has a latching or memory function, and polar responsive properties, respectively.

Thus, once the device described has been switched to one of the two states or conditions (i) and (ii) set out above, by the flow of control current of first or second polarities through winding W3, the device will remain in the condition to which switched, even though the control current may thereafter be removed or even when such current comprises a pulse of current. For example, upon the failure of the alternating current supply, when such supply is thereafter restored, even though the control current may not be restored or even when such current comprises a pulse of current, the device will still respond to the condition to which it was last switched, because the remanent magnetism of the electromagnet EM and the permanent magnet M will provide a memory of such condition.

It will be appreciated, therefore, that the device may be employed in a system for switching between conditions (i) and (ii) in response to the polarity of direct current control signals supplied thereto and that, where there is a failure of the alternating current supply, the device will store its last instruction, or any instruction fed to it during the failure, so that when the alternating current supply is restored the device will provide the desired condition (i) or(ii).

While I have shown and described but one form of apparatus embodying my invention, it is to be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. An alternating current switching device comprising:

(a) a rectangular shaped core of a material having high permeability characteristics,

(b) a Winding arrangement on first and second opposite limbs of said core and connected in series with a source of alternating current and a load,

(c) a permanent magnet having pole pieces so arranged in relation to a third limb of said core as to induce flux in a predetermined direction in the limbs of said core, and

(d) an electromagnet having a core of a material having remanent magnetic characteristics and pole pieces arranged in relation to the fourth limb of the first mentioned core so as to induce fiux in the limbs of such core in a direction to aid or oppose the flux induced by the permanent magnet in the limbs of that core according as a pulse of direct current of a first or a second polarity is supplied to the electro magnet, the core of said electromagnet maintaining a predetermined flux level upon the interruption of said pulse of direct current to control the power to said load from said source of alternating current between on and off states according to the polarity of the direct current pulse last supplied to said electromagnet.

2. A memory device for switching a source of alternating current connected across a load to on and off states according to the polarity of the last direct current control signal supplied thereto, said device comprising:

(a) a rectangular shaped core of a material having high permeability characteristics, and having first and second opposite limbs, and third and fourth opposite limbs,

(b) first and second windings on said first and second limbs, respectively, and connected to each other in series aiding flux relationship and in series with said load and said source of alternating current,

(0) a first magnet having pole pieces located in relation to the ends of the third limb of said core so as to induce flux in a predetermined direction through said core, and

(d) a second magnet having a core of a material having remanent magnetic characteristics, a winding, and pole pieces located in relation to the ends of the fourth limb of the first mentioned core so as to induce flux in such core in a direction to aid or oppose the fiux induced by the first magnet according as direct current of a first or second polarity is supplied to the last mentioned winding, the core of the second magnet substantially maintaining its fiux level upon the interruption of said direct current to retain the net flux relationship of said device according to its last energized state.

3. An alternating current switching device comprising in combination:

(a) a four-limbed rectangular core of a material having high permeability characteristics,

(b) a U-shaped permanent magnet having pole pieces adjacent the ends of one limb of said core and separated therefrom by adjustable air gaps, said magnet operating to induce flux in a predetermined direction in said core and of a value in accordance with the adjustment of said air gaps,

(c) a U-shaped electromagnet having pole pieces located adjacent the ends of the limb of said core opposite said one limb, a core of a material having remanent magnetic characteristics, and a Winding adapted to receive direct current of first or segmd polarities, the electromagnet operating to induce flux in the first mentioned core in said predetermined direction or in a direction opposite to said predetermined direction according to the polarity of direct current last supplied to said winding,

(d) a source of alternating current,

(e) a load device, and

(f) first and second windings on third and fourth limbs, respectively, of the first mentioned core, said windings connected in series with said source of alternating current and said load device, and also connected to each other so as to produce series aiding fluxes in the first mentioned core when such core is other than saturated.

4. An alternating current switching device comprising in combination:

(a) a four-limbed rectangular core of a material having high permeability characteristics,

(b) first and second windings arranged on first and second opposite limbs of said core so as to produce when energized series aiding fluxes in said core,

(c) a load device,

(d) a source of alternating current connected in series with said load device and said windings,

(e) a permanent magnet having pole pieces located in relation to the ends of a third limb of said core so as to produce a predetermined flux in the core, and

(f) an electromagnet having a core of a material having remanent magnetic characteristics, a winding adapted to receive direct current, and pole pieces located in relation to the ends of the fourth limb of the first mentioned core so as to produce flux in such core in a direction to oppose or aid the flux produced in that core by the permanent magnet according to the polarity of direct current last supplied to the electromagnet winding.

References Cited by the Examiner UNITED STATES PATENTS Dowling 340-174 Cohen et al 340-174 Williamson 30788 X Devol 340174 IRVING L. SRAGOW, Primary Examiner. 

1. AN ALTERNATING CURRENT SWITCHING DEVICE COMPRISING: (A) A RECTANGULAR SHAPED CORE OF A MATERIAL HAVING HIGH PERMEABILITY CHARACTERISTICS, (B) A WINDING ARRANGEMENT ON FIRST AND SECOND OPPOSITE LIMBS OF SAID CORE AND CONNECTED IN SERIES WITH A SOURCE OF ALTERNATING CURRENT AND A LOAD, (C) A PERMANENT MAGNET HAVING POLE PIECES SO ARRANGED IN RELATION TO A THIRD LIMB OF SAID CORE AS TO INDUCE FLUX IN A PREDETERMINED DIRECTION IN THE LIMBS OF SAID CORE, AND (D) AN ELECTROMAGNET HAVING A CORE OF A MATERIAL HAVING REMANENT MAGNETIC CHARACTERISTICS AND POLE PIECES ARRANGED IN RELATION TO THE FOURTH LIMB OF THE FIRST MENTIONED CORE SO AS TO INDUCE FLUX IN THE LIMBS OF SUCH CORE IN A DIERCTION TO AID OR OPPOSE THE FLUX INDUCED BY THE PERMANENT MAGNET IN THE LIMBS OF THAT CORE ACCORDING AS A PULSE OF DIRECT CURRENT OF A FIRST OR A SECOND POLARITY IS SUPPLIED TO THE ELECTROMAGNET, THE CORE OF SAID ELECTROMAGNET MAINTAINING A PREDETERMINED FLUX LEVEL UPON THE INTERRUPTION OF SAID PULSE OF DIRECT CURRENT TO CONTROL THE POWER TO SAID LOAD FROM SAID SOURCE OF ALTERNATING CURRENT BETWEEN ON AND OFF STATES ACCORDING TO THE POLARITY OF THE DIRECT CURRENT PULSE LAST SUPPLIED TO SAID ELECTROMAGNET. 